(1) A numerical procedure has been developed to describe the simultaneous transport of heat, chemical mass, and soil moisture in unsaturated soils. The deterministic model has been used to simulate transport of PCBs through different soils during light and moderate rain over 60 days. For unreactive chemicals, transport strongly depends on hydrodynamics and adsorptivities to different soil components. (2) In conjunction with an Interregional Research Unit of the WHO/UNEP/ILO International Programme on Chemical Safety (IPCS), a workshop is being planned for May 1985. The workshop has three major objectives: (a) to review current knowledge on groundwater contamination; (b) to review current knowledge on the adverse effects of individual chemicals and chemical mixtures observed in ground water; and (c) to provide guidance to Member States confronted with groundwater contamination and decontamination problems. (3) For the 3rd Workshop of the Scientific Group on Methodologies and Safety Evaluation of Chemicals (SGOMSEC) to develop methods for testing chemical mixtures, a manuscript was prepared that reviewed and analyzed mathematical models used to predict ground level concentrations of atmospheric pollutants during photochemical smog incidents.